This study is an investigation of the role of the outer membrane, specifically, the capsular polysaccharide of Vibrio parahaemolyticus, a human enteropathogen in adherence to epithehial cells. Capsular polysaccharide has been produced, purified from culture supernatant fluids by Cetavlon precipitation, re-precipitation from ethanol, hot phenol-water extraction and Sephadex gel chromatography. This material contains fucose, galactose, sialic acid and uronic acids. It is immunogenic in rabbits and does not induce antibody to the homologous O antigen. The role of capsular polysaccharide in adherence by V. parahaemolyticus is being explored by use of an in vitro human fetal intestinal cell model of bacterial adherence.